Reassessment of Australia's Oldest Freshwater Snail, Viviparus
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CSIRO PUBLISHING www.publish.csiro.au/journals/mr Molluscan Research, 2003, 23, 149–158 Reassessment of Australia’s oldest freshwater snail, Viviparus (?) albascopularis Etheridge, 1902 (Mollusca:Gastropoda:Viviparidae), from the Lower Cretaceous (Aptian, Wallumbilla Formation) of White Cliffs, New South Wales Benjamin P. KearA,B, Robert J. Hamilton-BruceA,E, Brian J. SmithC and Karen L. Gowlett-HolmesD ASouth Australian Museum, North Terrace, Adelaide, SA 5000, Australia. BSchool of Biological, Earth and Environmental Science, University of New South Wales, Sydney, NSW 2052, Australia. CQueen Victoria Museum, Wellington Street, Launceston, Tasmania 7250, Australia. DCSIRO Division of Marine Research, GPO Box 1538, Hobart, Tasmania 7001, Australia. ETo whom correspondence should be addressed. Email: [email protected] Abstract Viviparus (?) albascopularis Etheridge, 1902 is Australia’s oldest documented fossil freshwater gastropod. The taxon was established on the basis of a single opalised shell from the Lower Cretaceous (Aptian) marine deposits of the Wallumbilla Formation (Doncaster Member) at White Cliffs, New South Wales. Reassessment indicates that original placement in the caenogastropod family Viviparidae is justified; however, the specimen is reassigned to the endemic Australian genus Notopala Cotton, 1935 on the basis of shell morphology and close morphometric similarity to extant species. Implications for the origins and current distribution of Australian viviparid taxa are discussed. MR03003 ReB.et asseP.al Kearssm . ent of Vi viparus (?) al bascopul aris Etheridge Introduction The fossil record of Australian Cretaceous non-marine gastropods is depauperate and very poorly known. Nearly all the currently identified material has been recovered from the middle–upper Albian (Lower Cretaceous) fluviatile–lacustrine deposits of the Griman Ck Formation at Lightning Ridge in north-western New South Wales (NSW). This assemblage comprises primarily viviparids, although numerous other groups, including thiarids (Hamilton-Bruce et al. in press), succinids, camaenids (currently under study) and amphibolids (B. J. Smith, R. J. Hamilton-Bruce and B. P. Kear, unpublished data) are also present (Dettman et al. 1992; Smith 1999; Hamilton-Bruce et al. 2002). The only other documented Australian Cretaceous non-marine gastropod fossil is a single opalised shell (AM F17456) from the Aptian (Lower Cretaceous) marine sediments of the Wallumbilla Formation (Doncaster Member) at White Cliffs, NSW (Burton and Mason 1998: see figs 1,2 for detailed geological and locality maps of the area). This specimen was described (from a private collection belonging to a Mr H. Y. L. Brown of Adelaide, later acquired by the Australian Museum) by Etheridge (1902) and tentatively assigned to Viviparus (?) albascopularis, recognising similarity to members of the currently extant caenogastropod family Viviparidae. The present paper provides a revised description of the holotype (AM F17456) and only known specimen of V. (?) albascopularis Etheridge and reinterprets its taxonomic placement. Implications for the origins and distribution of Australian viviparid taxa are discussed. The Lower Cretaceous (Aptian) opal-bearing deposits of White Cliffs have long been known as a productive locality for fossils. Anderson (1892) briefly remarked on the presence of mollusc remains, crinoids and wood. Jaquet (1893) recorded belemnitid © Malacological Society of Australasia 2003 10.1071/MR03003 1323-5818/03/020149 150 Molluscan Research B. P. Kear et al. cephalopods and Devonian invertebrate fossils preserved as impressions in large erratic clasts. These were interpreted as a product of reworking from underlying Palaeozoic conglomerates. Etheridge (1897, 1902, 1904) reported the occurrence of bivalves, ammonites, naticid gastropods, plesiosaurs and ichthyosaurs. More recent studies by White (1926), Molnar (1980, 1991) and Kemp (1991) have also identified lungfish and dinosaur remains. Viviparus (?) albascopularis Etheridge is currently the oldest known Australian fossil freshwater gastropod and one of the earliest members of the Viviparidae. Today, this cosmopolitan family comprises various taxa, characterised by medium–large-sized turbiniform shells, possessing a rounded body whorl, moderately high and pointed spire, wide, round aperture and a concentric, horny operculum (Smith 1992). Within Australia, the distribution of the group is limited to a few species occurring in the large drainage basins that span much of the arid centre, northern tropical and coastal regions. The fossil record for Viviparidae is known from the Jurassic–Recent (Viviparus Montfort, 1810), with a tentative report based on an internal shell mold (?Bernicia Cox, 1927), possibly of marine origin, from the Early Carboniferous of England (Brookes-Knight et al. 1960). The group’s Australian record is very sparsely documented. Cotton (1935) described a species of Notopala Cotton, 1935 (N. wanjacalda) from upper Pleistocene sediments along the Murray River, near Sunnyside, South Australia (SA), and noted a second taxon (Notopala sp.) from the same deposit, which showed strong similarity to the extant N. hanleyi (von Frauenfeld, 1862). Dettman et al. (1992) reported viviparid snail shells from the Lower Cretaceous (middle-upper Albian) deposits of Lightning Ridge, NSW, as did Smith (1999), who also recorded representatives of the Naticidae, Thiaridae and Ellobiidae. Recently, Hamilton-Bruce et al. (2002) described a new genus (Albianopalin) and two new species of viviparid from Lightning Ridge, as well as indeterminate material attributable to the currently extant endemic Australian taxon Notopala. Other Australian non-marine gastropod fossils (all of Tertiary age) have been documented by Chapman (1937), McMichael (1968), Archer et al. (1994), Arena (1997) and Pledge et al. (2002). Occurrences from elsewhere in Australasia are rare, particularly in Cretaceous sediments. Some of the few examples include viviparids (genera uncertain) and thiarids (?Melanoides Olivier, 1804) from the Cenomanian–?Santonian (Upper Cretaceous) of New Zealand (Henderson et al. 2000) and possible thiarids (Pyrgulifera Meek, 1871) from both the Campanian–lower Maastrichtian (Upper Cretaceous) of the Chatham Islands (Stilwell 1998) and ?Campanian of New Caledonia (Henderson et al. 2000). Material and methods Material registered as the holotype of V. (?) albascopularis Etheridge includes a single shell with broken aperture margin and protoconch (AM F17456), preserved entirely in potch (non-precious or common opal). The specimen is derived from an unknown mine locality in the opal-bearing deposits of White Cliffs near Wilcannia in north-western NSW. The lithostratigraphic nomenclature for Lower Cretaceous rocks of the White Cliffs area was recently discussed by Burton and Mason (1998), who placed them within the Doncaster Member of the Wallumbilla Formation (Eromanga Basin), a unit of Aptian–middle Albian (115–approximately 100 million years ago; sensu Lowrie et al. 1980) age. However, the White Cliffs opal-bearing sediments are regarded as representing only the lower Aptian section of the Doncaster Member and comprise predominantly sandy/silty claystone and fine-grained sandstones deposited in a near-shore coastal marine setting (Burger 1988; Burton and Mason 1998). Determinations of palaeolatitude place the White Cliffs area as high as 70°S during the Early Cretaceous (Embleton 1984). Palaeoclimatic indicators for the region also suggest predominantly cool, strongly seasonal conditions with winter freezing (Frakes and Francis 1988, 1990; Sheard 1990; Frakes et al. 1995; De Lurio and Frakes 1999; Henderson et al. 2000). Estimates of sea level isotopic palaeotemperatures in the south-western section of the Reassessment of Viviparus (?) albascopularis Etheridge Molluscan Research 151 Eromanga Basin have yielded averages as low as 12.2°C (Stevens and Clayton 1971; Dettman et al. 1992). However, Selwood et al. (1994) reported revised isotopic data supporting much cooler ocean temperatures during the Early Cretaceous. Indeed, Pirrie et al. (1995) indicated palaeotemperatures of around 10°C based on Early Albian belemnites from the Carnarvon Basin, Western Australia (situated at approximately 45° palaeolatitude during the Cretaceous). In contrast, Huber et al. (1995) and Huber and Hoddell (1996) argued that minimal pole-to-equator thermal gradients existed during much of the Middle–Late Cretaceous. This was also discussed by Henderson et al. (2000), who noted that although palaeotemperatures at 70°–80° latitude would certainly have been more equitable than they are today, evidence such as the distinct growth-banding in Australian Cretaceous wood (Dettman et al. 1992), and the presence of potentially ice-rafted quartzite/porphyritic boulders (Frakes and Francis 1988, 1990; Frakes et al. 1995) and glendonites (crystal aggregates pseudomorphing the calcium carbonate hexahydrate mineral ikaite; Sheard 1990; DeLurio and Frakes 1999) attests to the strong seasonality and winter freezing along the inboard extremity of the Australian epicontinental seaway during the Aptian. Shell diameters were measured using the method of Boycott (1928), defined as ‘… the greatest dimension that can be found starting with the edge of the lip to a point on the opposite side of the shell on the last whorl’. Shell measurements were made to the nearest 0.05 mm using dial calipers. The Australian Museum, Sydney is abbreviated as AM throughout.